1. Field of the Invention
The present invention relates to a lens barrel, and in particular, relates to a lens barrel, or a zoom lens barrel, in which a plurality of movable members are moved by a common rotational ring (e.g., cam ring).
2. Description of the Related Art
In the retractable zoom lens (zoom lens barrel) disclosed in United States Patent Application Publication No. 2004/0160683 A1 (Japanese Patent No. 4,050,239), movement of a lens group frame, which holds the frontmost lens group, and an external ring (light-shielding decorative barrel), which is positioned radially outside the lens group frame, in an optical axis direction are controlled by different cam grooves formed on the outer peripheral surface of a cam ring. These cam grooves are formed to move the lens group frame and the external ring in the optical axis direction in the same moving manner in the photographing range (zooming range) of the zoom lens; however, these cam grooves are formed into different shapes so as to make the lens group frame and the external ring produce a relative movement therebetween when the zoom lens moves from a ready-to-photograph state to the retracted state (fully retracted state) and vice versa. The zoom lens is provided at the front end of the external ring with a lens barrier mechanism for opening and shutting the front end aperture of the zoom lens in front of the frontmost lens group. In the retracted state of the zoom lens, in which the barrier blades of the lens barrier mechanism are shut, the frontmost lens group is moved rearward relative to the lens barrier mechanism to so that the frontmost lens group is prevented from interfering with the barrier blades of the lens barrier mechanism. On the other hand, in a ready-to-photograph state of the zoom lens, in which the barrier blades are fully opened, the frontmost lens group is advanced relative to the lens barrier mechanism to prevent rays of light incident on the frontmost lens group from being intercepted by the lens barrier mechanism (especially the inner edge of the front end aperture).
In the retractable zoom lens disclosed in United States Patent Application Publication No. 2004/0160683 A1, each of the cam grooves for guiding the frontmost lens group that are formed on a cam ring basically traces the moving path of the frontmost lens group. Namely, to correspond to the non-linear moving path of the frontmost lens group in the optical axis direction in the zooming range, each of the cam grooves for guiding the frontmost lens group also has a non-linear cam track that does not have constant inclination angle relative to the circumferential direction of the cam ring. In the case of forming cam grooves having different shapes on the same peripheral surface of the cam ring, the efficiency of space utilization is improved (the area for formation of the cam grooves is reduced) by positioning these cam grooves as closely as possible to each other, which contributes to miniaturization of the cam ring. However, if the cam grooves have a non-linear cam track, each cam groove easily interferes with the other cam groove; and additionally, it has been difficult to position the plurality of cam grooves formed on the same peripheral surface of the cam ring closely to one another so as to have a minimum distance therebetween.